If your default search engine keeps suddenly switching to Yahoo even though you traditionally use Chrome, Safari, or Firefox to browse the web, your computer is probably infected with malware. Manually resetting your browser settings should prevent Yahoo redirect virus from clogging your system. 8th
How to get rid of Yahoo on Chrome?
(top right in Google Chrome), select Settings, in the Search engines section click Manage search engines…, in the opened list look for Search. Find yahoo.com, click the three vertical dots next to that URL and choose Remove from List. 12